In a vehicle equipped with fuel cells as an electric power source, several control devices (systems) have been proposed to utilize the waste heat of the fuel cells for heating in air conditioning equipment. One proposed system includes a circuit for making a circulated flow of a cooling medium between the fuel cells and a radiator (for the convenience sake, this circuit is referred to as ‘cooling circuit’ in the following explanation) and a circuit for making a circulated flow of the cooling medium through a heater core used for heating (for the convenience sake, this circuit is referred to as ‘heating circuit’ in the following explanation). When the temperature of the fuel cells is within a specific temperature range with a high power generation efficiency of the fuel cells (for example, a temperature range of 72° C. to 80° C., hereafter referred to as ‘high efficiency temperature range’), this prior art system interconnects and links these two circuits to utilize the waste heat of the fuel cells for heating up the heater core via the circulated flow of the cooling medium. Another proposed system warms up the fuel cells in a low temperature environment, until the temperature of the fuel cells reaches the high efficiency temperature range.
The technique of interconnecting and linking the cooling circuit and the heating circuit in the state where the temperature of the fuel cells is within the high efficiency temperature range may be combined with the technique of warming up the fuel cells until the temperature of the fuel cells reaches the high efficiency temperature range. In this case, the waste heat of the fuel cells can not be utilized until the temperature of the fuel cells reaches the high efficiency temperature range. In response to the user's heating request given prior to an increase of the temperature of the fuel cells to the high efficiency temperature range, a different heating element, such as an electric heater, provided separately from the heater core should be activated to heat up the cooling medium flowing in the heating circuit. The electric power consumed by the electric heater is supplied from the fuel cells. Namely the fuel cells are required to generate the electric power that is to be supplied to the electric heater. This undesirably worsens the overall fuel consumption of the control device for the vehicle.
The prior art system allows flow interconnection and linkage of the cooling circuit and the heating circuit under a higher temperature condition than a warm-up termination temperature (a final temperature of the fuel cells attained by the warm-up). The temperature of the cooling medium in the heating circuit is generally lower than the temperature of the cooling medium in the cooling circuit in the state before the linkage of the heating circuit with the cooling circuit. The linkage of these two circuits causes a relatively low-temperature flow of the cooling medium to be flowed from the heating circuit into the cooling circuit. The temperature of the fuel cells may thus be decreased to be lower than the warm-up termination temperature. This damages the effectiveness of the warm-up and requires the use of the different heating element, such as the electric heater, to heat up the flow of the cooling medium in the state after the linkage of the heating circuit with the cooling circuit. This undesirably worsens the overall fuel consumption of the control device for the vehicle.